1. Field of the Invention
The present invention relates to a snowmobile capable of traveling on a snow field, with an engine as a drive source.
2. Description of the Background Art
In snowmobiles designed to travel by the power of an engine, a variety of construction styles and designs for the vehicle body frame have been proposed. For example, in U.S. Pat. No. 6,446,744, Wubbolts et al. disclose the construction of an engine cradle for such vehicles as snowmobiles, ATVs, and related vehicles.
In FIG. 19 of U.S. Pat. No. 6,446,744, the vehicle body frame of the snowmobile is formed by joining to each other a sub frame, left and right engine walls, and a tunnel frame composed of a top plate and side plates, in this order from the front side toward the rear side. It is shown in this reference that the engine is mounted on central portions of the left and right engine walls of the vehicle body frame from the upper side.
In recent years, there have been an increasing number of cases where a comparatively heavy 4-cycle engine is adopted for use in a snowmobile, in place of a comparatively lightweight 2-cycle engine. When the heavy 4-cycle engine is used in these vehicles, it is preferable to enhance the rigidity of the vehicle body frame.